The medical term for a "sore throat" is pharyngitis. We owe the word "pharyngitis" to gifts from the Greeks: "pharynx" meaning "the throat" + the suffix"-itis" denoting inflammation. So pharyngitis literally means inflammation of the pharynx.
Like the thigh bone, the pharynx is connected not to the hip bone, but to a remarkable number of other structures including the mouth and nose, the esophagus and larynx, and (via the Eustachian tubes) the ears. That is why sore throats so often involve these other structures.
And that's not all. The pharynx has additional neighbors of renown, namely the nubbins of lymphatic tissue in the back of the pharynx called the "tonsils"and the rings of like tissue higher up in the nasal portion of the pharynx called the "adenoids".
Inflammation of the pharynx causes it to redden and swell which may make breathing and swallowing more difficult. Another features may be an "exudate" or whitish-yellow covering, especially pronounced on the tonsils. The exudate contains dead cells and bacteria or viruses.
The most common cause of pharyngitis is infection by a virus, especially one of the viruses that can cause the common cold. A number of viruses including those blamed for influenza ("flu") and infectious mononucleosis ("mono") and a class of viruses called adenoviruses can cause particularly severe inflammation of the pharynx.
The notorious "strep throat" is due to a bacterial infection of the pharynx. The offending bacteria is the streptococcus.
It is crucial that the diagnosis of strep throat be made because of the many complications that can ensue, among them rheumatic fever with inflammation of the joints and heart valves, glomerulonephritis with sometimes serious disease of the kidneys, and scarlet fever.
A strep throat can closely mimic a viral sore throat (and vice versa). Throat culture has been the gold standard for telling the difference. The throat culture proves the diagnosis of a strep. New tests have been developed which give quicker results.
Treatment of strep throat with antibiotics may not always significantly shorten the course of the disease. What antibiotics do is to kill the bacteria and cut down the risk of the dreaded complications.
Other bacteria such as the one responsible for diphtheria also cause pharyngitis. So can microorganisms like the yeast Candida. Thus a "simple" sore throat, may not always be so simple!